In food processing plants, food packaging manufacturing plants and the like, the interior of the factory building is kept at positive pressure by setting air pressure in the factory building to be higher than external pressure, with a view to preventing contamination of the factory building by outside germs. When introducing outside air (air outside the factory building) into the factory building, therefore, the air is introduced after being filtered to remove as many germs and the like as possible (see for instance, Patent document 1).
Meantime, large amounts of PET bottles for a beverage container have been produced in recent years, on account of such advantages as their lightweight and easy handling.
These PET bottles are obtained by blow molding, which involves manufacturing first a primary molding called a perform by injection molding, followed by heating of the preform at a temperature that enables orientational drawing of the preform. The molding equipment for PET bottles used during blow molding is roughly split between a heating zone where the preforms are heated, and a blow molding zone where the heated preforms are blow-molded. The interior of the heating zone is heated up to a predetermined temperature, whereupon the preforms are introduced into the zone and are heated up to a temperature that allows orientational drawing. In case of fluctuations in the temperature in the factory building where the blow molding equipment is installed, which causes the atmosphere temperature in the blowing equipment to fluctuate as well, there may occur changes in the measured values of bottles, which are the final shapes, even if the temperature of the preforms and the temperature of the blow molding mold stand at a set temperature. The temperature of outside air varies substantially depending on the season. Therefore, when filtered outside air is to be introduced into the factory building, various schemes are adopted so as to keep the interior of the factory building at a constant temperature, for instance by installing air conditioning equipment in the factory building.
Herein, when a large amount of air from inside the factory building is to be discharged outside and a large amount of outside air is introduced into factory building in its stead, it becomes necessary to install large air conditioning equipment and filters having a large filtering surface area at multiple sites in order to quickly adjust the temperature in the factory building to a predetermined temperature. The associated extra cost undermines the economic logic of this approach. An easily conceivable alternative involves discharging out air from inside the factory building by small amounts, and introducing in its stead outside air into the factory building, by small amounts. However, doing so necessitates filtering and air conditioning equipment, and so this approach is no different from the above-described one.
To keep the interior of the heating zone at a predetermined temperature, the air heated in the heating zone is discharged into the factory building lying outside the zone. Discharging heater air into the factory building, however, causes the temperature in the factory building to rise, which deteriorates the working environment. The temperature could be kept constant by introducing outside air, but doing so would entail arranging filtering equipment (filters) and air conditioning equipment at multiple sites, as is the case above.
Known equipment used in the biaxial stretch blow molding includes, for instance, an air conditioner for injection stretch blow molding machines in which an injection molding station where preforms are molded is isolated, by way of an isolating sheet, from a blow molding station where preforms are stretch-blown, in order to prevent that dew condensation arises on the injection mold and affects the preform molding, and in which air having had the dryness thereof increased is blown again into the injection molding station, to prevent dew condensation on the injection mold (for instance, Patent document 2).
When the temperature of the outside air fluctuates, the temperature of the blow molding machine installed in the building fluctuates likewise, as a result of which there varies the atmosphere temperature in the blow molding machine, and there may vary also the measurement values of bottles, which are the final shapes, even if the temperature of the preforms and the temperature of the mold for blow molding are at a set temperature. It becomes thus difficult to produce bottles stably.    Patent document 1: Japanese Patent Application Laid-open No. 2006-52873    Patent document 2: Japanese Patent Application Laid-open No. 2000-202895